Isolation and physical characterization of membrane proteins remains a central challenge in biomolecular science. Isolating membrane proteins and obtaining their crystal structures is important to furthering an understanding of their function and role in metabolic pathways. The lack of sufficient methods for membrane protein isolation, purification, and crystallization represents a significant hindrance to fundamental and applied biological research because these proteins perform so many crucial functions in vivo. Membrane proteins are difficult to manipulate and ultimately crystallize because these macromolecules are rarely soluble in simple aqueous buffers.
Solubilizing membrane proteins for physical characterization and crystallization requires that the membrane protein be combined with a synthetic amphiphile, typically a detergent. The resulting crystal is generally a protein-detergent complex rather than the protein alone. The detergent therefore plays an important role in determining whether high quality crystals will form. High quality crystals are essential for structural determination and characterization, such as by X-ray crystallography.
Three-dimensional structure determination for membrane proteins has been successful only within the past two decades, and the set of known membrane protein structures is far smaller than the set of known soluble protein structures. Synthetic amphiphiles, such as detergents, are crucial tools in this field. They are used to extract embedded proteins from the membranes in which they naturally occur and to maintain native protein conformation in the solubilized state. Physical characterization is often carried out with protein-amphiphile complexes, and such complexes are usually the basis for crystallization efforts. Growth of high-quality crystals is typically the rate-limiting step in structure determination.
Although more than 120 detergents are commercially available, membrane protein manipulation is still challenging. Many membrane proteins tend to denature and aggregate in these commercially available detergents. Thus, it is of great interest to develop novel classes of amphiphiles with enhanced properties in terms of solubilization and stabilization to aid fundamental and applied protein research. Preferably, the amphiphiles could be synthesized from readily available starting material by convenient protocols. The practical aspects of such agents would significantly increase their utility.